The overall objective or long-term goal of the proposed research is the clinical and theoretical evaluation of the electrical impedance technique as a harmless, noninvasive method of localizing, quantitating, and monitoring intrathoracic fluid volumes (pleural effusion, pericardial effusion, pulmonary engorgement, and pulmonary edema) in man and animals. In the electrical impedance method, a low-intensity (4 mA @ 100 kHz) constant current is applied to the thorax by means of two electrodes placed on the surface of the neck and abdomen, and changes in potential which reflect shifts in impedance are measured between a second pair of electrodes on the thorax. In the dog, changes in the value of the basal impedance of the thorax will be measured during the infusion of known volumes of exogenous fluid (saline, plasma, and blood). Similarly, the changes in impedance associated with shifts of endogenous plasma and blood will be determined. The changes in impedance associated with blood and plasma within the pericardial cavity will be measured as will the changes in impedance accompanying pulmonary edema produced by one of three methods: (1) the intravenous administration of alloxan, (2) the intrabronchial instillation of sucrose, or (3) lavage of the lungs with saline. Various electrode arrays will be studied with regard to their sensitivity in both detecting and localizing known fluid accumulations within the thorax.